1. Field of the Invention
The present invention relates generally to print media transport systems and, more specifically, to a method and apparatus for transporting a sheet of print media through a hard copy apparatus transport path with limited surface contact to protect the printing or printed surface.
2. Description of Related Art
Many computer-controlled hard copy printing apparatus are commercially available. Some types are compatible with specially coated media; for example, ink-jet printers use special media to print photographic quality reproductions from digitized photographs. [The art of ink-jet technology is relatively well developed. Commercial products such as computer printers, graphics plotters, copiers, and facsimile machines employ ink-jet technology for producing hard copy. The basics of this technology are disclosed, for example, in various articles in the Hewlett-Packard Journal, Vol. 36, No. 5 (May 1985), Vol. 39, No. 4 (August 1988), Vol. 39, No. 5 (October 1988), Vol. 43, No. 4 (August 1992), Vol. 43 No. 6 (December 1992) and Vol. 45, No. 1 (February 1994) editions. Ink-jet devices are also described by W. J. Lloyd and H. T. Taub in Output Hardcopy [sic] Devices, chapter 13 (Ed. R. C. Durbeck and S. Sherr, Academic Press, San Diego, 1988). For convenience in describing the art and the present invention, all types of hard copy apparatus are sometimes hereinafter referred to as xe2x80x9cprinters;xe2x80x9d all types, sizes, and compositions of print media are also referred to as xe2x80x9cpaper,xe2x80x9d all compositions of colorants are sometimes referred to as xe2x80x9cink;xe2x80x9d and all embodiments of an ink-jet writing instrument are simply referred to as a xe2x80x9cpen;xe2x80x9d no limitation on the scope of the invention is intended nor should any be implied.
In many printers, the input paper pathxe2x80x94that is, the automated, paper-transport path between the input tray where the user stacks sheets of preferred paper for the next printing job and the printing station of the apparatusxe2x80x94is configured to be curvilinear in order to reduce the overall printer footprint. U.S. Pat. No. 5,481,408 (assigned to the common assignee herein and incorporated herein by reference) filed by Giles et al. on Apr. 30, 1993 for a DUAL FEED PAPER PATH FOR INK-JET PRINTER, FIG. 7, demonstrates such a typical system as would be found in a commercial DeskJet(trademark) product by Hewlett-Packard Company. However, contact with stationary printer mechanisms such as guide surfaces in the transport path can damage coatings on the paper printing surface, thus affecting the quality of the printed image. Maintaining a substantially constant tension in a moving sheet of paper presents many problems and can require a complex drive system; see e.g., U.S. Pat. No. 5,495,276 filed on Apr. 18, 1994 by Mul et al. (assigned to the common assignee herein) for a UNIFORM MEDIA TENSIONING OF PRINT MEDIA DURING TRANSPORT IN LASER PRINTER.
A common solution in a curvilinear input paper path is to underdrive an upstream set of transport rollers and overdrive a downstream set of transport rollers to relieve the tension during the curved path segment with the sheet moving between guide frames. This type of subsystem adds mechanical and electrical complexity and increases cost of manufacture as separate motors and controls are required to appropriately bend or buckle the media to avoid printing surface contact with a guide frame.
Therefore, there is a need for improved methods and apparatus for moving special media through an input paper path between stationary guide frame members to avoid a friction producing contact between the printing surface of the media and the frame.
In its basic aspects, the present invention provides a print media transport device including: a curved frame defining a media path therein; mounted with respect to the path, a pair of upstream rollers and a pair of downstream rollers, the upstream pair having one driven roller; a flexible coupling between the one driven roller and a pulley roller of the downstream pair; and a selectively positionable mechanism for changing tension of the flexible coupling such that predetermined shaping and positioning of media is maintained in the path.
In another basic aspect, the present invention provides a method for guiding print media, having a coated printing surface and a non-printing reverse surface, through a curvilinear path without contacting the coated printing surface on stationary mechanisms. The method includes the steps of: receiving a leading edge of a sheet of the media in a nip between an actively driven roller of a first pair of media drive rollers at the ingress of the curvilinear path such that the reverse surface is guided along a curved surface defining the path; receiving the leading edge of the sheet in a nip between a second pair of media drive rollers at the egress of the curvilinear path; and upon receiving the leading edge in the nip between the second pair of media drive rollers, changing the tension of a drive belt to a pulley wheel coupled to the driven roller to underdrive the second pair of media drive rollers such that the sheet is buckled in order to pass through the path without contact of the coated printing surface with any upper curved surface defining the path.
In another basic aspect, the present invention provides a printer having a printing zone therein, including: a supply of sheets of print media; an ink-jet writing instrument mounted for depositing ink on a sheet in the printing zone; and a print media transport device for sequentially delivering picked sheets to the printing zone, the device including a first curved frame member and a second curved frame member defining a curvilinear print media path therebetween, a first set of media drive rollers having a first drive roller and a first pinch roller mounted upstream of the print media path, a second set of media drive rollers having a second drive roller and a second pinch roller mounted downstream of the print media path, a motor coupled one drive roller, a flexible coupling between the first drive roller and the second drive roller, and a selectively positionable mechanism for changing tension of the flexible coupling such that a predetermined buckling of a segment of the print media in the path between the first curved frame member and second curved frame member is maintained wherein there is no contact between a surface of the media to be printed and a surface of either curved frame member.
Some of the advantages of the present invention are:
it simplifies input paper path tension control;
it simplifies the electronic control requirements;
it reduces the number of drive motors required for paper tension control;
it reduces manufacturing complexity and costs; and
it is adaptable for use with a duplex path media paper source.
The foregoing summary and list of advantages is not intended by the inventor to be an inclusive list of all the aspects, objects, advantages and features of the present invention nor should any limitation on the scope of the invention be implied therefrom. This Summary is provided in accordance with the mandate of 37 C.F.R. 1.73 and M.P.E.P. 608.01(d) merely to apprise the public, and more especially those interested in the particular art to which the invention relates, of the nature of the invention in order to be of assistance in aiding ready understanding of the patent in future searches. Other objects, features and advantages of the present invention will become apparent upon consideration of the following explanation and the accompanying drawings, in which like reference designations represent like features throughout the drawings.